A typical two port pump impeller includes a suction eye having two ports opening into opposing expanding chambers. The ports have smaller openings than the single, axial opening of the suction eye due to the fact that each port handles one half of the total flow. Solids which are sufficiently small to enter the suction eye axial opening may be too large to pass through either port, eventually significantly plugging the impeller. Stringy material may have one end drawn into one port and the other end drawn into the other port. Thus, the material may be draped around the base edge of an impeller vane. More stringy materials can be built up thusly and the ports can become substantially clogged. Furthermore, even if the materials impeding flow through the ports don't completely clog the impeller, these materials may cause the pump impeller to be out-of-balance, resulting in pump vibration.
To alleviate these problems, a single port centrifugal pump impeller is used for solids-handling pumps, i.e., pumps which must handle liquids with entrained solid matter. A single port impeller eliminates clogging in solid-handling pumps, particularly pumps handling stringy materials. The single radial passage through the impeller can be substantially the same size as the opening of the suction eye of the impeller, so that any object entering the pump will pass completely through the impeller without clogging. There are no impeller parts for stringy material to hang on which would restrict flow through the impeller.
One drawback of a single port centrifugal impeller is that, unless countermeasures are taken, the impeller is inherently out of dynamic balance. To compensate for this imbalance, balance weight can be added to dynamically balance the impeller. However, improper balancing can detrimentally effect efficiency. Also, the balanced impeller cannot always be trimmed easily to create new head and flow conditions without altering its dynamic balance.
U.S. Pat. No. 1,439,365 describes a single port impeller which uses a liquid filled chamber to balance the impeller. The chamber must be filled with liquid through a hole, which is then plugged.
U.S. Pat. No. 1,470,607 describes a single port impeller which incorporates small blades or vanes arranged in opposition to the single port. The small blades function to impart an additional impulse to the liquid in the pump casing and to balance the heavy metal formation surrounding the mouth of the port. These small blades allow the impeller to be trimmed, by turning the impeller in a lathe. In the turning operation, meal is also removed from the small blades or vanes, the amount being proportionate to the amount removed from the body of the impeller. This is intended to preserve the dynamic balance of the impeller. This patent also describes the impeller having a closed chamber which is filled with liquid through a hole, thereafter plugged, to balance the impeller.
The present invention recognizes that it would be advantageous to provide a single port impeller for a solids-handling pump which remains in dynamic balance even if the impeller is trimmed on a lathe, and which impeller is resistant to cavitation, and which impeller is cost effectively manufactured.